1. Field of the Invention
The invention relates to an actuator as stated in the preamble of claim 1 for operating a positioning element.
Actuators are used in furniture, hospital beds, patient lifts etc. Actuators have also found their way into the industrial sector, where they for example are applied in manufacturing equipment and solar panels. In a particular embodiment, the actuators are designed as motor operators for operating switchgears used in mains power distribution systems. The invention thus further relates to an actuator embodied as a motor operator as stated in the preamble of claim 2 for opening and closing a mains switch of switchgear in mains power distribution systems such as public medium high voltage distribution systems.
2. Description of the Prior Art
Actuators embodied as motor operators for switchgears are known, see e.g. U.S. Pat. No. 4,804,809 to Chance Co. AB, U.S. Pat. No. 5,254,814 to Chance Co. AB, WO 2008/052548 A1 to Linak A/S and WO 2006/106364 to Viserge Ltd. These motor operators are separate units for mounting in front of switchgears as indicated in U.S. Pat. No. 4,804,809 to Chance Co. AB and WO 2006/106364 to Viserge Ltd. The motor operators are contained in a weather and vandal proof enclosure which is rather voluminous. Further, it should be fully operable under all weather conditions and operate in a reliable manner. The front surface of the switchgear is exposed to the open air which is why the overall size of the motor operator is of no significant importance. However, a type of switchgear is also known where the front surface is covered by a front door to protect the front surface of the switchgear and to prevent unauthorized access to the switchgear. The front door restricts the space available for a motor operator and further complicates the mounting as it is prohibited to make bores and weldings in the switchgear cabinet.
It should also be taken into account that the motor operator may be activated either locally or remotely to open and close the mains switch of the switchgear. In some cases there could be a need to perform a manual operation of the switchgear. This could be in case of a failure, damage or breakage of the transmission line (e.g. cables) in the supply network for example due to excavations. It could also be in case of a faulty motor operator, or when service personnel on site wishes to manually operate the switchgear and perform service on the transmission line. In that case the transmission line has to be connected to the earth potential by operating the earth switch of the switchgear. In many types of switchgears, this action can only be performed when the switchgear state is open and the handle tool for the mains switch is pulled out. This means that the motor operator will have to demount from the switchgear. For operating the switchgear operating shaft, a spring has to be suppressed, before the power of the spring is released in the transition operation of the mains switch. Removing the motor operator when the spring is not in its relaxed state will be a difficult task and could lead to a sudden release of the spring and cause a rotation of the operating shaft and should be avoided. It is therefore common to use motor operators, where the self-locking mechanism of the motor operator can be released. This also complicates the construction of the motor operator and contributes to the overall size. Such rather voluminous type of switchgear is found in WO 97/16660 to ABB Kraft A/S disclosing a worm gear based power transmission device having a spring based disengagement mechanism, whereby the device when not driven by a motor may be manually operated. However, this device constitutes a rather bulky construction, which is difficult to retrofit. Consequently, the device is also difficult to dismount so as to allow manual operation of the switchgear.
Another worm gear based motor operator having smaller dimensions is disclosed in WO 2010/034313 A2 to Linak A/S. Its small size and the fact that the operator unit and the motor driving the unit are two separate units make it very easy to retrofit. This motor operator can be manually operated, first by loosening a retainer element whereby the worm gear is released and secondly by dismounting the operator unit. Remounting the operator unit and reconnecting it is, however, a time-consuming and cumbersome task. Further, by loosening the retainer element a number of balls are brought out of engagement with the worm wheel, whereby the worm wheel is released. After release, the retainer element cannot simply be tightened again as the balls need to be rearranged in a corresponding number of holes in the worm wheel. This may therefore require that the motor operator is serviced by authorized personnel. This could therefore further increase the downtime of the switchgear. When remounting the motor operator, it could be problematic to align the position of the coupling part of the motor operator and the position of the operating shaft of the switchgear. Hence, there is a need for a motor operator which overcomes these problems associated with the known motor operators.
It is an object of the present invention is to provide a motor operator for use in a switchgear having small dimensions, low costs, and which in a simple, reliable and quick manner may be disconnected so as to allow manual operation of the switchgear.